Outboard motor

ABSTRACT

A power transmitting portion of an outboard motor has a power transmitting shaft connected to an output shaft of an engine to rotate together therewith, an oil pump disposed on the power transmitting shaft, and a driving force acquisition mechanism arranged to acquire driving force from the power transmitting shaft. The power transmitting portion is able to provide an outboard motor capable of ensuring a pump discharge amount without incurring an increase in the pump size and the oil amount.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an outboard motor including a transmission device arranged to change the speed of rotation of an engine and to transmit the rotation to a propeller.

2. Description of the Related Art

An outboard motor including a hydraulic clutch type transmission mechanism which shifts the speed of rotation of an engine between high speed and low speed positions and transmits the rotation to a propeller, an oil pump supplying hydraulic pressure to the hydraulic clutch type transmission mechanism, and a hydraulic pressure control valve controlling hydraulic pressure supplied to the hydraulic clutch type transmission mechanism is known in the art. See, for example, WO 2007-007707 A1.

There are cases in which increasing the oil drawing rate of an oil pump is desired when the oil pump is disposed as close to an oil reservoir as possible in outboard motors including the hydraulic clutch type transmission mechanism, for example. However, if the oil pump is disposed adjacent to the oil reservoir, rotation of the engine that is reduced by the transmission mechanism is transmitted to the oil pump, thus causing a fluctuation of the rotational speed of the oil pump. Therefore, it is necessary to increase the size of the oil pump and the oil amount to an oil pan. This results in an undesirable increase in the cost and weight of the outboard motor.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide an outboard motor capable of ensuring a stable pump discharge amount without incurring increases in oil pump size and an oil amount.

A first preferred embodiment of the present invention provides an outboard motor including an engine arranged to generate power in which a crankshaft is vertically oriented, and a transmission device connected to the crankshaft and arranged to change the speed of rotation of the engine and transmit the rotation to a propeller, in which the transmission device includes a power transmitting portion connected to the crankshaft and a speed changing portion connected to the power transmitting portion, and the power transmitting portion includes a power transmitting shaft connected to an output shaft of the engine to rotate together therewith and an oil pump disposed on the power transmitting shaft.

A second preferred embodiment of the present invention provides the outboard motor in accordance with the first preferred embodiment, in which the power transmitting portion includes a driving force acquisition mechanism arranged to acquire driving force from the power transmitting shaft, a first housing, a second housing housed in the first housing to house the oil pump, and a third housing connected to the first housing to house the driving force acquisition mechanism.

A third preferred embodiment of the present invention provides the outboard motor in accordance with the second preferred embodiment, in which a relief passage arranged to fluidly connect a section for an oil discharge passage and a section for an oil drawing passage together is arranged in the second housing, and a relief valve which opens when pressure in the relief passage exceeds a predetermined value is interposed in the relief passage.

A fourth preferred embodiment of the present invention provides the outboard motor in accordance with the third preferred embodiment, in which the oil discharge passage and the oil drawing passage are provided on one side in the watercraft width direction of a straight line extending in a traveling direction through the power transmitting shaft.

In the outboard motor in accordance with the first preferred embodiment of the present invention, the oil pump is disposed on the power transmitting shaft rotating together with the engine thus preventing fluctuation of the ratio between the rotational speed of the oil pump and the engine speed. This facilitates setting of the oil amount corresponding to each engine speed and stable securing of a required pump discharge amount.

In the second preferred embodiment of the present invention, the driving force acquisition mechanism arranged to acquire driving force is provided on the power transmitting shaft. Therefore, engine power can be acquired from the power transmitting shaft separately from the oil pump, and a driving force proportional to the rotational speed of the engine can be acquired. As a result, an acquired driving force can be used for a wider range of purposes. For example, it is possible to secure a sufficient amount of coolant supply to the engine and so forth in the case that a coolant pump is connected to the driving force acquisition mechanism.

The second housing in which the oil pump is housed is connected to the first housing connected to the engine inside the first housing. The third housing in which the driving force acquisition mechanism is housed is connected to the first housing outside the first housing. Therefore, two mechanisms of the oil pump and the driving force acquisition mechanism can be compactly housed, thus facilitating assembly.

In the third preferred embodiment of the present invention, the relief passage is arranged in the second housing which houses the oil pump, and the relief valve is interposed in the relief passage. Therefore, the relief valve can be disposed in the second housing utilizing an open space, thus achieving a downsizing of the whole power transmitting portion.

In the fourth preferred embodiment of the present invention, the oil discharge passage and the oil drawing passage are provided on one side in the watercraft width direction of the straight line extending in the traveling direction through the power transmitting shaft. Therefore, the oil drawing passage and the oil discharge passage can be disposed on the front side and the rear side, respectively, in a rotational direction of the oil pump. Accordingly, an oil line configuration can be simplified. Oil is directly drawn from a section in which oil collects, thereby allowing for a reduction in the length of a drawing line to the oil pump. Consequently, this allows for a significant reduction in the total amount of oil and in the size of the oil pump, thus achieving a cost savings.

Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an outboard motor including a transmission device in accordance with a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional rear view of a transmission device in accordance with a preferred embodiment of the present invention.

FIG. 3 is a cross-sectional front view of a transmission device in accordance with a preferred embodiment of the present invention.

FIG. 4 is a cross-sectional view of a power transmitting portion in which an oil pump of a transmission device is disposed in accordance with a preferred embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 2.

FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 2.

FIG. 7 is a side view of a housing in which a transmission device is housed in accordance with a preferred embodiment of the present invention.

FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 7.

FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8.

FIG. 10 is a cross-sectional view taken along line X-X in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described hereinafter with reference to attached drawings.

FIGS. 1 through 10 are drawings for describing an outboard motor in accordance with preferred embodiments of the present invention. Front, rear, right, and left in descriptions of the preferred embodiments denote front, rear, right, and left in the view as seen from the rear of a watercraft unless otherwise specified.

In the figures, reference numeral 1 denotes an outboard motor installed in a stern 2 a of a hull 2. The outboard motor 1 is supported swingably in the vertical direction by a clamp bracket 3 fixed to the hull 2 via a swivel arm 4 and supported to be steerable to the right and left via a pivot portion 5.

The outboard motor 1 has an engine 6 arranged to generate power, an exhaust guide 7, a cowling 8, an upper case 9, and a lower case 10.

The engine 6 includes a vertically oriented crankshaft 6 a disposed in a generally vertical direction, and is mounted on the exhaust guide 7. The cowling 8 is installed on an upper surface of the exhaust guide 7 to cover an outer periphery of the engine 6. The upper case 9 is connected to a lower surface of the exhaust guide 7. The lower case 10 is connected to a lower surface of the upper case 9.

The outboard motor 1 is supported by the clamp bracket 3 via an upper mount member 11 mounted on the exhaust guide 7 and a lower mount member 12 mounted on a lower end of the upper case 9.

The outboard motor 1 includes a transmission device 15 arranged to change a speed of rotation of the engine 6 and transmit the rotation to a propeller 13. The propeller 13 is attached to a propeller shaft 13 a. The propeller shaft 13 a is disposed in the lower case 10 to be perpendicular to the crankshaft 6 a. The propeller shaft 13 a is connected to a drive shaft 14 coaxially disposed with the crankshaft 6 a via a bevel gear mechanism 13 b.

The transmission mechanism 15 includes a first input shaft (power transmitting shaft) 24 defining a portion of a power transmitting portion connected to the crankshaft (output shaft) 6 a of the engine 6, a planetary gear type transmission mechanism (speed changing portion) 20 connected to the first input shaft 24, and a forward-reverse switching mechanism 21 connected to the transmission mechanism 20.

The transmission mechanism 15 is housed in a generally cylindrical housing 22 that is oil-tight and the housing 22 is housed in the upper case 9 to be positioned in a front portion thereof in the traveling direction. An exhaust system 16 arranged to discharge exhaust gas from the lower case 10 into water is disposed in the rear of the transmission device 15 in the upper case 9.

The housing 22 is divided into an upper housing 22 a in which the transmission mechanism 20 is housed and a lower housing 22 b in which the forward-reverse switching mechanism 21 is housed (as shown in FIG. 2).

The planetary gear type transmission mechanism 20 has a first internal gear 25, a first sun gear 27, a first output shaft 28, a first carrier 29, first planetary gears 30, and a second clutch 31.

The first internal gear 25 is connected to the first input shaft 24 to rotate together therewith. The first sun gear 27 is connected toward the housing 22 via a first clutch 26. The first output shaft 28 is coaxially disposed with the first input shaft 24. The first carrier 29 is connected to the first output shaft 28 to rotate together therewith. The first planetary gears 30 are supported by the first carrier 29 to be capable of relative rotation and are meshed with the first sun gear 27 and the first internal gear 25. The second clutch 31 is installed between the first sun gear 27 and the first carrier 29.

The first input shaft 24 is coaxially disposed with the crankshaft 6 a and combined with the crankshaft 6 a to rotate together therewith.

The first sun gear 27 is housed in the housing 22. The first sun gear 27 is connected to a support housing 33 rotatably supporting the first output shaft 28 or disconnected from the support housing 33 via the first clutch 26.

The first clutch 26 is a one-way type clutch which only permits rotation of the first sun gear 27 in rotational direction (a) (clockwise) of the crankshaft 6 a but prohibits rotation in the opposite direction (counterclockwise).

The second clutch 31 preferably is a wet type multi-plate clutch, for example, and has a clutch housing 31 a, clutch plates 31 b, a piston 31 e, and a spring member 31 c.

The clutch housing 31 a is combined with the first sun gear 27 to rotate together therewith. The clutch plates 31 b are disposed between the clutch housing 31 a and the first carrier 29. The piston 31 e is disposed in a hydraulic chamber 31 d formed in the clutch housing 31 a and brings the clutch plates 31 b into contact with each other with hydraulic pressure supplied to the hydraulic chamber 31 d in a direction to transmit power. The spring member 31 c urges the piston 31 e in a direction to disconnect power transmission.

When an operator of a watercraft operates a shift lever (not shown) or a shift operation switch (not shown) to a low speed position, the first clutch 26 is engaged, the first sun gear 27 is locked, and the second clutch 31 is disengaged. When rotation of the engine 6 is transmitted from the first input shaft 24 to the first internal gear 25 in this state and the internal gear 25 rotates, each of the planetary gears 30 rotates itself, and rotates relatively to the first internal gear 25, and revolves with respect to the first sun gear 27. Thereby, the speed of the engine rotation is reduced and the rotation is transmitted to the first output shaft 28.

On the other hand, when operation is switched to a high speed position, the first clutch 26 is disengaged, the first sun gear 27 enters a free state, and the second clutch 31 is engaged. When rotation of the engine 6 is transmitted from the first input shaft 24 to the first internal gear 25 in this state, the first internal gear 25, each of the first planetary gears 30, and the first sun gear 27 rotate unitarily. Thus, rotation of the first input shaft 24 is transmitted to the first output shaft 28 without speed reduction.

The forward-reverse switching mechanism 21 has a second internal gear 36, a second input shaft 37, a second output shaft 38, a second sun gear 39, a second carrier 40, a second planetary gear 41, a third planetary gear 42, and a fourth clutch 43.

The second internal gear 36 is connected to the housing 22 via a third clutch 35. The second input shaft 37 is coaxially disposed with the first output shaft 28 and connected to the first output shaft 28 to rotate together therewith. The second output shaft 38 is coaxially disposed with the second input shaft 37. The second sun gear 39 is unitary and integral with and connected to the second output shaft 38. The second carrier 40 is connected to the second input shaft 37 to rotate together therewith. The second planetary gear 41 is rotatably supported by the second carrier 40 and meshed with the second sun gear 39. The third planetary gear 42 is meshed with the second internal gear 36. The fourth clutch 43 is installed between the second carrier 40 and the second output shaft 38.

The fourth clutch 43 and the third clutch 35 preferably are, for example, wet type multi-plate clutches having constructions generally similar to the second clutch 31 described above.

When a forward-reverse switching lever (not shown) or a forward-reverse switching switch (not shown) is in a neutral position, the third and fourth clutches 35 and 43 are disengaged. The second input shaft 37 idles. Rotation of the second input shaft 37 is not transmitted to the second output shaft 38.

When shifting from the neutral position to a forward position, the third clutch 35 is disengaged, and the fourth clutch 43 is engaged. The second internal gear 36, the second and third planetary gears 41 and 42, and the second sun gear 39 unitarily rotate. The second output shaft 38 rotates in the forward travel direction which is the same as rotational direction (a) (shown in FIG. 5) of the engine 6.

On the other hand, when shifting from the neutral position to a reverse position, the third clutch 35 is engaged, and the fourth clutch 43 is disengaged. The second internal gear 36 is fixed to the housing 22 to be unable to rotate. The second and third planetary gears 41 and 42 revolve while rotating in directions opposite to each other. The second sun gear 39 rotates in the opposite direction. Thereby, the second output shaft 38 rotates in the reverse travel direction which is the direction opposite to rotational direction (a) of the crankshaft 6 a.

The transmission device 15 has a planetary gear type speed reducing mechanism 18 arranged to reduce the speed of rotation of the second output shaft 38 and transmitting the rotation to the drive shaft 14.

The speed reducing mechanism 18 has an internal gear 55 connected to the second output shaft 38 to rotate together therewith, a planetary gear 57 meshed with the internal gear 55 and rolling on the internal gear 55, and a sun gear 58 meshed with the planetary gear 57 and disposed to be unable to rotate.

The speed reducing mechanism 18 has a speed reducer housing 56 fixed to the lower case 10 and rotatably supporting a boss 55 a of the internal gear 55 and a carrier 59 rotatably supporting the planetary gear 57.

The sun gear 58 is fixed to the lower case 10 to be unable to rotate. The carrier 59 is rotatably supported by the sun gear 58. The carrier 59 is combined with the drive shaft 14 to rotate together therewith.

The transmission device 15 includes the first input shaft 24 defining the power transmitting portion, an oil pump 45 disposed on the first input shaft 24, and a driving force acquisition mechanism 46 arranged to acquire driving force from the first input shaft 24, and preferably has the following specific construction.

The oil pump 45 supplies hydraulic pressure to the second through fourth clutches 31, 35, and 43 and supplies oil for lubricating and cooling each sliding portion of the transmission device 15. The oil pump 45 is independent from an oil pump supplying lubricating oil to each sliding portion of the crankshaft 6 a and so forth of the engine 6.

The first input shaft 24 extends upward from the housing 22 and is housed in a first housing 47 connected to an upper surface of the housing 22. A second housing 48 arranged to house the oil pump 45 is disposed in and fixed to the first housing 47. The first input shaft 24 is rotatably supported by the second housing 48.

The third housing 49 arranged to house the driving force acquisition mechanism 46 is connected to the outside of the first housing 47. The third housing 49 is disposed to extend outward on the starboard side of the first housing 47 in the watercraft width direction.

The driving force acquisition mechanism 46 has a driving force acquisition shaft 46 a extending in a direction toward the starboard side and perpendicular to the axis of the input shaft 24. The driving force acquisition shaft 46 a is connected to the first input shaft 24 to rotate together therewith via a bevel gear mechanism 46 b.

A water pump 50 is connected to the driving force acquisition mechanism 46. The water pump 50 is disposed in the third housing 49 in parallel, or substantially in parallel, with the driving force acquisition shaft 46 a and has a pump shaft 52 on which a reduction gear 52 a meshed with driving gear 46 c of the driving force acquisition shaft 46 a is arranged and a pump cover 51 housing the water pump 50. The pump cover 51 is detachably connected to the third housing 49.

Coolant drawn up by the water pump 50 and some of the coolant is supplied to the engine 6 side by a coolant hose 51 a connected to the pump cover 51. The remaining coolant is supplied to the transmission device 15 side by a branch hose 51 b connected to the coolant hose 51 a.

Coolant jackets 22 c and 22 d (shown in FIG. 5) extending in the circumferential direction are arranged on the starboard and the rear sides of the housing 22. The branch hose 51 b is connected to the coolant jackets 22 c and 22 d.

The oil pump 45 is housed in a pump chamber 48 a arranged in the second housing 48 and has an inner rotor 45 a combined with the first input shaft 24 to rotate together therewith and an outer rotor 45 b fixed to the second housing 48. The oil pump 45 pressurizes and discharges oil drawn by rotation of the inner rotor 45 a.

An oil inlet 48 b fluidly connected to a suction port of the oil pump 45 and an oil outlet 48 c fluidly connected to a discharge port are arranged in the second housing 48.

An oil reservoir 22 e is defined at a bottom of the housing 22. The oil reservoir 22 e and the oil inlet 48 b are fluidly connected together by an oil drawing passage 22 f arranged in the housing 22 and extending in the axial direction.

An oil discharge passage 22 g extending in parallel, or substantially in parallel, with the oil drawing passage 22 f is arranged in the housing 22. An upstream end of the oil discharge passage 22 g is fluidly connected to the oil outlet 48 c. A downstream end thereof is fluidly connected to hydraulic chambers 31 d, 35 d, and 43 d of the second through fourth clutches 31, 35, and 43 via respective clutch hydraulic passages 22 i.

The oil drawing passage 22 f and discharge passage 22 g are disposed on the port side in the watercraft width direction with respect to a straight line “A” (shown in FIG. 5) extending in the traveling direction through the center of the first input shaft 24. In addition, the oil drawing passage 22 f is disposed in a portion downstream of the oil discharge passage 22 g in rotational direction (a) of the crankshaft 6 a, that is, on a front side in the traveling direction.

An oil return passage 22 h extending in the circumferential direction along the inside of the coolant jacket 22 c is arranged on the side generally opposite to the oil drawing passage 22 f across the second input shaft 37 in the lower housing 22 b. The oil return passage 22 h is fluidly connected to the oil reservoir 22 e.

Oil passages 24 a, 28 a, 37 a, and 38 a are arranged to be fluidly connected to each other in the axes of the first input shaft 24, the first output shaft 28, the second input shaft 37, and the second output shaft 38, respectively. Oil supplied from the oil outlet 48 c to the oil passages 24 a, 28 a, 37 a, and 38 a is supplied to each of bearings, sliding portions, and so forth.

In this case, oil supplied into the upper housing 22 a returns to the oil reservoir 22 e through the oil return passage 22 h of the lower housing 22 b. Oil supplied into the lower housing 22 b drops and returns to the oil reservoir 22 e.

A relief passage 48 d fluidly connecting the oil discharge passage 22 g and the oil drawing passage 22 f together is arranged in the second housing 48. A relief valve 61 is arranged in the relief passage 48 d. The relief valve 61 is urged in the closing direction by a spring member 62 whose elastic force is set so that the relief valve 61 opens when pressure in the relief passage 48 d exceeds a predetermined value (see FIG. 6).

The transmission device 15 includes second through fourth hydraulic pressure control valves 65, 66, and 67 arranged to control hydraulic pressure supplied to the second through fourth clutches 31, 35, and 43, respectively, of the planetary gear type transmission mechanism 20 and the forward-reverse switching mechanism 21 independently of each other.

Each of the second through fourth hydraulic pressure control valves 65 through 67 is controlled by a controller (not shown) to open or close based on a speed shifting signal, a forward-reverse switching signal, and so forth.

The hydraulic pressure control valves 65 through 67 are housed in respective hydraulic housing 65 a through 67 a defined independently of each other. The hydraulic housing 65 a through 67 a have respective housing main bodies 65 b through 67 b detachably mounted on a left side wall surface 22 k of the housing 22 preferably by a plurality of bolts 68, for example, inserted from the outside and respective lid members 65 c through 67 c detachably mounted on the housing main bodies 65 b through 67 b in a state that the hydraulic valves 65 through 67 are fixed preferably by a plurality of bolts 69, for example, inserted from the front side.

Each of the hydraulic pressure control valves 65 through 67 is disposed in parallel, or substantially in parallel, in the vertical direction on the port side in the watercraft width direction of the housing 22 and is disposed to protrude outward from the housing in the watercraft width direction.

Each of the hydraulic pressure control valves 65 through 67 is disposed on the side opposite to the water pump 50 across the center line C of the transmission device and is positioned below the water pump 50 in a view from the rear of the watercraft (see FIG. 2). This stabilizes the weight balance between the left and the right sides of the transmission device 15.

Each of the hydraulic pressure control valves 65 through 67 is positioned above the lower mount member 12 in a view from a side of watercraft (see FIG. 7). Thereby, each of the hydraulic pressure control valves 65 through 67 can be disposed without interfering with the lower mount member 12. This allows prevention of an increase in the size of the upper case 9 in the watercraft width direction and downsizing of the whole outboard motor 1.

The hydraulic pressure control valves 65 through 67 have respective valve shafts 65 d through 67 d whose axes are disposed in the fore-and-aft direction that is the watercraft traveling direction and respective electric drivers 65 e through 67 e connected to front sides of the respective valve shafts 65 d through 67 d and reciprocally driving the valve shafts 65 d through 67 d in the axial directions.

A hydraulic circuit 70 and a coolant circuit 71 are defined in a mating surface between the left side wall surface 22 k of the housing 22 and each of the hydraulic housings 65 a through 67 a. Here, since the hydraulic circuits 70 and the coolant circuits 71 of the second through fourth hydraulic pressure control valves 65 through 67 have similar constructions, descriptions will be made only about the hydraulic circuit 70 and the coolant circuit 71 of the fourth hydraulic pressure control valve 67 arranged to control hydraulic pressure supplied to the fourth clutch 43, that are shown in FIG. 8.

The coolant circuit 71 is arranged to cool the hydraulic valve 67 by injecting oil. Specifically, hydraulic cooling passages 22 q and 67 j fluidly connected to the oil discharge passage 22 g are arranged to extend in the watercraft width direction in the housing 22 and a hydraulic housing 67 a. The hydraulic cooling passage 67 j opens toward the driver 67 e in the hydraulic housing 67 a.

Oil pressurized by the oil pump 45 passes through the oil discharge passage 22 g and the hydraulic cooling passages 22 q and 67 j and is injected to the driver 67 e, thereby cooling the driver 67 e. The oil injected to the driver 67 e returns into the housing 22 via a return passage 67 k formed in the hydraulic housing 67 a.

The hydraulic circuit 70 is constructed to disconnect or connect hydraulic pressure to the fourth clutch 43 and specifically has the following construction.

As shown in FIG. 8, the clutch hydraulic passage 22 i defined in the housing 22 is bifurcated into a hydraulic pressure input passage 22 m fluidly connected to the oil discharge passage 22 g and a hydraulic pressure output passage 22 n fluidly connected to the hydraulic chamber 43 d of the fourth clutch 43.

A hydraulic pressure input passage 67 f fluidly connecting the valve shaft 67 d of the hydraulic pressure control valve 67 and the hydraulic pressure input passage 22 m together and a hydraulic pressure output passage 67 g fluidly connecting the valve shaft 67 d and the hydraulic pressure output passage 22 n together are defined in the hydraulic housing 67 a.

Hydraulic pressure releasing passages 22 p and 67 h arranged to release hydraulic pressure supplied to the hydraulic chamber 43 d are arranged in the housing 22 and the hydraulic housing 67 a. Hydraulic pressure passes through the hydraulic pressure releasing passage 67 h and 22 p and returns into the housing 22.

The hydraulic pressure input passages 22 m and 67 f, the hydraulic pressure output passages 22 n and 67 g, and the hydraulic pressure releasing passages 22 p and 67 h are arranged to extend in directions perpendicular or substantially perpendicular to the axis of the valve shaft 67 d.

Hydraulic pressure pressurized by the oil pump 45 is supplied to the hydraulic pressure input passages 22 m and 67 f through the oil discharge passage 22 g. The hydraulic pressure input passage 67 f is blocked by the valve shaft 67 d. Thereby, the fourth clutch 43 is disengaged.

When the valve shaft 67 d of the hydraulic pressure control valve 67 operates and the hydraulic pressure input passage 67 f opens, hydraulic pressure is supplied to the hydraulic chamber 43 d of the fourth clutch 43 through the hydraulic pressure output passage 67 g. Thereby, the fourth clutch 43 is engaged. The hydraulic pressure input passage 67 f is blocked when the valve shaft 67 d returns to the original position. Hydraulic pressure in the hydraulic chamber 43 d is released into the hydraulic housing 67 a through the hydraulic pressure releasing passages 67 h and 22 p.

In accordance with the present preferred embodiment, the oil pump 45 is disposed on the first input shaft 24 connected to the crankshaft 6 a of the engine 6 to rotate together therewith. Therefore, the rotational speed of the oil pump 45 is the same as the rotational speed of the crankshaft 6 a, thus securing a required pump discharge amount without incurring increase in the pump size and the oil amount.

In this preferred embodiment, the driving force acquisition mechanism 46 arranged to acquire driving force from the engine 6 is connected to the first input shaft 24. Therefore, engine power can be directly acquired from the first input shaft 24 separately from the oil pump 45. The engine power is a driving force proportional to the rotational speed of the engine 6 and with small fluctuation. Accordingly, the driving force can be used for a wider range of purposes. In this preferred embodiment, the water pump 50 is connected to such a driving force acquisition mechanism 46, thus securing a sufficient amount of coolant supply to the engine 6 and so forth.

In this preferred embodiment, the first housing 47 housing the first input shaft 24 is connected to the housing 22. The second housing 48 housing the oil pump 45 is connected to the first housing 47 inside of the first housing 47. The third housing 49 housing the driving force acquisition mechanism 46 is connected to the starboard side of the first housing 47 in the watercraft width direction to protrude outward. Therefore, two mechanisms of the oil pump 45 and the driving force acquisition mechanism 46 can be housed compactly. Further, this facilitates assembling of the first through third housings 47 through 49.

In this preferred embodiment, the relief passage 48 d fluidly connecting the oil discharge passage 22 g and the oil drawing passage 22 f together is defined in the second housing 48 housing the oil pump 45. The relief valve 61 is interposed in the relief passage 48 d. Therefore, the relief valve 61 is disposed in the second housing 48 housing the oil pump 45 by effectively utilizing on open space, thus allowing downsizing of the whole transmission device 15.

In this preferred embodiment, the oil discharge passage 22 g and the oil drawing passage 22 f are disposed on the port side of the straight line “A” extending in the traveling direction through the center of the first input shaft 24. Therefore, the oil drawing passage 22 f and the oil discharge passage 22 g are disposed on the front side and the rear side, respectively, in rotational direction (a) of the oil pump 45, thereby achieving a simple configuration of the oil line. Oil is directly drawn up from the oil reservoir 22 e, thereby allowing reduction in the length of the drawing line to the oil pump 45. As a result, this allows for reduction in the total amount of oil and in the size of the oil pump 45, thus achieving cost saving.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. An outboard motor comprising: an engine arranged to generate power including a vertically oriented crankshaft; and a transmission device connected to the crankshaft and arranged to change a speed of rotation of the engine and transmit the rotation to a propeller; wherein the transmission device includes a power transmitting portion connected to the crankshaft and a speed changing portion connected to the power transmitting portion; and the power transmitting portion includes a power transmitting shaft connected to an output shaft of the engine to rotate together therewith, and an oil pump disposed on the power transmitting shaft.
 2. The outboard motor according to claim 1, wherein the power transmitting portion includes: a driving force acquisition mechanism arranged to acquire driving force from the power transmitting shaft; a first housing; a second housing housed arranged in the first housing and arranged to house the oil pump; and a third housing connected to the first housing and arranged to house the driving force acquisition mechanism.
 3. The outboard motor according to claim 2, wherein a relief passage arranged to fluidly connect an oil discharge passage and an oil drawing passage together is defined in the second housing, and a relief valve which opens when pressure in the relief passage exceeds a predetermined value is interposed in the relief passage.
 4. The outboard motor according to claim 3, wherein the oil discharge passage and the oil drawing passage are provided on one side in a watercraft width direction of a straight line extending in a traveling direction through the power transmitting shaft. 